1. Field of the Invention
The present invention relates to an improved magneto-optical recording and reproducing device in which a bias magnetic field is applied and a modulated laser beam is irradiated to record a signal by a slight rotation of a polarized plane of a reflected beam at a recording point on a disc and the reverse bias magnetic field is applied and the laser beam is irradiated to erase the signal. The focus of the laser beam is controlled by a magnetic field and a current produced by an actuator, and a laser irradiating carriage is linearly moved by a linear motor.
2. Description of the Prior Art
A conventional recording and reproducing device is illustrated in FIGS. 1 and 2 where FIG. 1 illustrates a recording condition and FIG. 2 illustrates an erasing condition.
Referring to FIG. 1, a recording surface of a magneto-optical disc 1 is formed of a magnetic thin film of TbFeCo alloy, or the like. A signal is recorded by slightly rotating a polarized plane of a reflected beam in a direction related to a magnification while a bias magnetic field having constant direction and a modulated laser beam are applied to the recording surface. The recorded signal is reproduced by means of a detector utilizing a polarizing beam splitter.
In contrast, referring to FIG. 2, the recorded signal is erased by applying a reverse bias magnetic field in a direction opposite to the bias magnetic field in the recording operation and irradiating a laser beam continuously to provide a polarized plane of a reflected beam in a uniform direction.
More specifically, in recording a signal on the magneto-optical disc 1, a magnetic field created by an electromagnet 2 is applied to a surface of the disc in advance so as to cause the side 1 of the magneto-optical disc to be, for example, an S pole, as illustrated in FIG. 1. An actuator for driving an objective lens so as to focus the lens on the recording surface of the magneto-optical disc is arranged on a carriage 3 carrying a laser irradiating apparatus. The actuator comprises magnets 4 and coils 5 which operate to focus the laser beam on the recording surface by driving the objective lens to or away from the magneto-optical disc 1 based on the current flowing in the coils 5. For driving the carriage, coils 6 respectively wound on yokes 8 are arranged on the carriage 3 and magnets 7 are linearly disposed respectively opposing the coils 6 with the same polarization as the coils. The carriage 3 is linearly driven by an attraction or repulsion between a current flowing in the coils 6 and the magnets 7 to radially drive a focused point of the laser beam on the recording surface of the turning magneto-optical disc 1. The laser beam is modulated and a signal is recorded on the recording surface of the magneto-optical disc 1 whether a polarized plane of the reflected beam is rotated or not.
On the other hand, as shown in FIG. 2, a recorded signal is erased by maintaining a polarized plane of a modulated reflected beam in a uniform direction by reversing a current flow in the magnet 2 so as to make the side of the magneto-optical disc 1 a N pole and irradiating a laser beam continuously on the surface. In such a magneto-optical recording and reproducing device, the magnets 4 of the actuator and the magnets 7 of the linear motor are disposed so that the N poles are symmetrical with respect to the center, as shown in FIG. 2.
In such a magneto-optical recording device, in the recording condition illustrated in FIG. 1, a closed magnetic path is formed between the electromagnet 2 and the magnets 4, 7, and consequently the magnetic fluxes of the electromagnet 2 and magnets 4, 7 pass through the magneto-optical disc 1 in the same direction so as to increase the total magnified flux and strengthen the magnetic field.
On the other hand, in the erasing condition illustrated in FIG. 2, the magnetic field created by the electromagnet 2 is in the opposite direction of the magnetic field created by the magnets 4, 7, and consequently the magnetic flux through the magneto-optical disc 1 decreases to weaken the magnetic field.
The difference of the magnetic force passing through the magneto-optical disc 1 between the recording condition and erasing condition is large, so that in the erasing condition it is necessary to strengthen the magnetic field by increasing the current flowing in the electromagnet 2. Therefore, a special circuit to control the current is required. Further, when the same amount of current flows in the electromagnet 2 during the recording and erasing condition, the magnetic field of the magnets 4, 7 must not influence the magnetic field of the electromagnet 2. Therefore, the distance between the electromagnet 2 and the magnets 4, 7 must be sufficiently large, or the magnets 4, 7 must be surrounded by a magnetic shield. The former results in the carriage becoming large in size requiring additional space and weight. The latter results requires a magnetic shield also resulting in additional weight.